CVE-2021-1718 in SharePoint Foundation
Summary
by MITRE • 01/13/2021
Microsoft SharePoint Server Tampering Vulnerability
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Analysis
by VulDB Data Team • 05/04/2025
The CVE-2021-1718 vulnerability represents a critical tampering flaw in Microsoft SharePoint Server that allows attackers to manipulate server-side components and potentially execute unauthorized operations. This vulnerability specifically affects SharePoint Server 2016 and SharePoint Server 2019 installations, creating a pathway for malicious actors to compromise the integrity of the platform's core functionalities. The flaw stems from insufficient validation of user input within the SharePoint Server's web application layer, enabling attackers to inject malicious payloads that can alter server behavior and data processing mechanisms. According to the Common Weakness Enumeration catalog, this vulnerability maps to CWE-20, which describes improper input validation, a foundational weakness that enables various attack vectors including code injection and data manipulation. The vulnerability is particularly concerning as it operates at the application layer where SharePoint Server handles user requests and processes web-based interactions, making it a prime target for attackers seeking persistent access to enterprise collaboration platforms.
The technical exploitation of CVE-2021-1718 occurs when an authenticated attacker with appropriate permissions can manipulate the SharePoint Server's internal processes through carefully crafted requests that bypass normal validation controls. This tampering capability allows adversaries to modify server-side operations, potentially altering how documents are processed, how user permissions are handled, and how data flows through the SharePoint infrastructure. The vulnerability manifests when the server fails to properly validate and sanitize input parameters that are passed to internal server components, creating opportunities for attackers to inject malicious code or manipulate existing server functions. Security researchers have identified that the flaw primarily affects SharePoint Server's web service endpoints that handle document management and user access controls, where insufficient sanitization allows for command injection and data manipulation attacks. The vulnerability's impact is amplified by the fact that SharePoint Server often serves as a central hub for enterprise document management and collaboration, making successful exploitation potentially devastating for organizational data integrity and security posture.
Operational impact of CVE-2021-1718 extends beyond immediate data compromise to encompass broader security implications for enterprise environments relying on SharePoint Server infrastructure. Organizations that fail to patch this vulnerability face risks of unauthorized data access, document manipulation, and potential lateral movement within their network infrastructure. The tampering capability creates opportunities for attackers to establish persistent backdoors, modify access controls, and potentially escalate privileges to gain administrative access to SharePoint Server environments. From an attacker's perspective, this vulnerability aligns with tactics described in the MITRE ATT&CK framework under the T1059.001 technique for command and scripting interpreter, as well as T1078.004 for valid accounts, since exploitation typically requires authenticated access but can lead to privilege escalation. The vulnerability's exploitation can result in significant business disruption, regulatory compliance violations, and potential data breaches that could affect sensitive corporate information, intellectual property, and customer data stored within SharePoint environments. Organizations with extensive SharePoint Server deployments face particularly high risk, as the centralized nature of the platform means that successful exploitation can affect multiple departments and business units simultaneously.
Mitigation strategies for CVE-2021-1718 should prioritize immediate implementation of Microsoft's security patches and updates released to address the specific validation flaws in SharePoint Server. Organizations must ensure that all SharePoint Server 2016 and 2019 installations are updated to the latest security releases, as Microsoft has provided comprehensive fixes that address the input validation issues enabling this vulnerability. Network segmentation and access control measures should be implemented to limit exposure of SharePoint Server environments to unauthorized users, while monitoring systems should be deployed to detect anomalous access patterns or manipulation attempts. Security teams should conduct thorough vulnerability assessments to identify any systems running unpatched SharePoint Server versions and implement additional controls such as web application firewalls to filter suspicious requests. Regular security audits of SharePoint Server configurations and access controls are essential to prevent exploitation attempts, while privileged access management solutions should be deployed to minimize the risk of unauthorized access to administrative functions. The remediation process should also include comprehensive testing of patches in controlled environments before full deployment to ensure compatibility with existing SharePoint Server functionalities and prevent operational disruptions. Organizations should also consider implementing multi-factor authentication and just-in-time access controls for SharePoint Server environments to add additional layers of security beyond the basic authentication mechanisms that may be exploited through this vulnerability.